Multiple purpose quick-changeover extrusion system

ABSTRACT

Improved, high-capacity extrusion systems ( 20, 220 ) are provided which minimize product losses and permit the user to conduct multiple, segregated short extrusion runs with a minimum of down time between runs. The systems ( 20, 220 ) include an extruder assembly ( 21, 221 ) having a special, multiple-position die assembly ( 28 ), as well as an upstream preconditioner ( 24 ) and feed bin assembly ( 22 ). A variable speed, variable output discharge screw feeder ( 78 ) is located between the preconditioner outlet ( 62 ) and extruder barrel inlet ( 90 ). A PLC-type controller ( 30 ) coupled to the extruder assembly components establishes a choke full condition at the discharge feeder ( 78 ) so that continuous uninterrupted flow of preconditioned material to the extruder ( 26 ) at a uniform mass flow rate is maintained for as long as possible. In preferred forms, load cells ( 46, 72 ) are operatively coupled to the bin assembly ( 22 ) and preconditioner ( 24 ) so as to monitor material flow through the systems ( 20, 220 ). A multiple stage cascade-type dryer assembly ( 29 ) is provided downstream of extruder ( 26 ). The assembly ( 29 ) is controlled via the controller ( 30 ) in coordination with the extruder assemblies ( 21, 221 ) so as to maintain the segregation between separate product runs throughout the drying operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is broadly concerned with extrusion systems andmethods characterized by a minimum of down time between individual runsand with comparatively little waste of starting materials during thecourse of the runs. More particularly, the invention is concerned withsuch methods and systems wherein the extrusion systems include apreconditioner and an extruder coupled in series with a variable speeddischarge device therebetween; in use, the systems are run so as tomaintain the discharge device in a full choke condition for as long aspossible so that the extruder receives material at a continuous andnon-varying rate throughout substantially all of a given run. Thisallows proper processing of almost all of the starting material whilepermitting rapid clearing of the system so that a new run can be almostimmediately commenced. In preferred forms, a staged verticalcascade-type dryer forms a part of the system and permits drying/coolingof the individual products from the extruder in a continuous and productsegregated fashion.

2. Description of the Prior Art

Extrusion systems have long been used for the production of a variety offood and other products. For example, many pet and human foods areproduced using such equipment. Many extrusion systems include apreconditioner and an extruder in series relationship. Dry materials arefed from a bin system into the preconditioner outlet, where thematerials are moisturized and partially cooked through application ofsteam and/or water and intense mixing. Such preconditioning materialsare then fed into the inlet of an extruder equipped with one or moreelongated, axially rotatable augers and an endmost apertured extrusiondie. In the extruder, the materials are subjected to intense heat,pressure and shear and are forced through the extrusion die for completecooking and shaping. Thereafter, the extruded products are typicallydried and cooled in a multiple-pass dryer.

While extrusion systems of this type are common, significant operationalproblems remain. One such issue is the amount of waste involved in anygiven production run. Specifically, at the start up of a run waste isgenerated while the system comes into equilibrium and essentiallycontinuous flow rates, pressures, temperatures, and residence times areestablished. Even more significant, however, is the waste problemencountered at the end of an extrusion run. Thus, when the last of aquantity of starting material is fed to the preconditioner, thereinevitably follows a period where the flow of material to the extruderfalls off until the preconditioner is emptied. Normally, the productproduced during this last run stage is unacceptable and must bediscarded. When it is considered that preconditioners hold from 900-1800pounds of material, it will be appreciated that the last-stage waste issignificant.

The above problem may not be deemed overly serious where largeproduction runs are involved. Thus, if a 40-ton run is scheduled, theloss of 1,000 pounds of starting material may be sustainable. However,there is an increasing tendency to schedule short production runs of5,000 pounds or less. In such cases the loss of 1,000 pounds at the endof the production run is economically unacceptable. This problem is soacute that some processors report that they obtain only a 60% yield on4-ton batch runs.

Another adverse factor in extrusion processing stems from the down timeassociated with run changeovers. That is, where a processor wishes tochange over a given system between two different products, down times ofan hour or more are not uncommon. Again, where large-volume runs arescheduled, an operator can live with long down times. However, if aseries of short (e.g., 5-ton or less) runs are scheduled on a productionday, it will be seen that the changeover problem becomes significant.

The short run phenomenon also has a potentially adverse consequence forthe post-extrusion drying operation. That is, the end-stage extrudatefrom a first run must not be allowed to commingle with the first-stageproduct from the next succeeding run. Therefore, unless special stepsare taken, the extruder must be shut down between runs to allowsufficient time for passage and clearance of all the extruded productthrough the dryer.

There is accordingly a need in the art for improved extrusion systemsand processes which overcome the problems outlined above and provide aquick changeover capability while also minimizing product loss.

SUMMARY OF THE INVENTION

The present invention overcomes the problems outlined above and providesimproved extrusion systems, components thereof, and methods. Broadlyspeaking, the extrusion systems of the invention include an extruderhaving an elongated barrel with at least one axially rotatable, flightedauger therein, with the barrel presenting an inlet and an outlet and adie mounted at the barrel outlet. Such systems also include apreconditioner having shiftable mixing elements therein and an inlet forreceiving material and an outlet coupled with the extruder barrel forfeeding preconditioning material to the latter. A bin assembly and avariable speed inlet feeder screw are also normally coupled with thepreconditioning inlet for feeding starting materials to thepreconditioner.

An important part of the extrusion systems of the invention involves theuse of a variable speed, variable output discharge feeder such as ascrew feeder between the preconditioner outlet and the extruder inlet.In order to maximize usage of starting material, the system is run sothat the screw feeder is maintained in a choke full condition for aslong as possible. In this way, a steady and substantially constant flowof preconditioned material is delivered to the extruder for finalprocessing. In order to accomplish this end, the control for the systemmay be set so as to alter preconditioner operation toward the end of agiven extrusion run. To give one example, where a horizontally orientedpreconditioner is employed the system may be set up so that, towards theend of the run, the preconditioner operation is altered to maintain thechoke full condition at the discharge feeder. Such alteration mayinvolve reversing the rotation of the preconditioner mixing paddles toforce more material forwardly to sustain the choke full condition.

In another related aspect of the invention, the extrusion systemsinclude one or more detectors coupled with a microprocessor controllersuch as a programmable logic controller (PLC). A detector assembly isoperatively associated with at least the preconditioner (and usually thebin assembly as well) in order to determine the flow rate of materialpassing therethrough. Preferably, the mass flow rate is determined, buta volumetric flow rate could also be measured. The controller can thenadjust system operation to maintain constant flow to the extruder for aslong as possible. Preferably, a first detector (preferably in the formof a weighing device such as a load cell) is coupled with the binassembly for determining when substantially the last of a predeterminedquantity of starting material has been fed to the preconditioner. Asecond detector (also preferably a load cell) is coupled with thepreconditioner and the two detectors are used to determine the flow ratethrough the preconditioner.

In order to further minimize down time, the systems of the inventionpreferably include a specialized multiple-position die assembly whichcan be rapidly shifted between first and second separate dies withoutthe need for laborious changeovers which stop production. The preferreddie assembly of the invention includes a head assembly including firstand second spaced outlets with individual die members coupled thereto. Ashiftable member such as a cylindrical rotor is located within the headand includes an elongated product-conveying passageway presenting aproduct inlet opening adjacent the extruder barrel outlet, and a spacedproduct outlet. A drive is connected to the shiftable member and isoperable to selectively move the passageway outlet between the first andsecond dies. In addition, a third discharge outlet is preferablyprovided between the die outlets. The drive can move the passagewayoutlet to the discharge position during the hiatus between product runsso that the extrusion system can be flushed and unwanted extrudatediscarded.

The extruder systems of the invention also preferably includes a dryer(preferably a multiple-stage cascade dryer) which receives extrudatefrom the extruder for drying and cooling. The operation of the dryer iscorrelated with the extruder operation so that products can becontinuously dried but in a segregated fashion, i.e., the product from afirst extrusion run is dried and maintained separate from the extrudatefrom a second extrusion run. Advantageously, the dryer is operativelycoupled to the PLC for the extruder and related equipment.

Use of the systems and methods of the invention affords numerousadvantages. Primary among these is the ability to process a salableproduct using a very high proportion of the starting materials. Forexample, where short product runs of up to about 10,000 pounds areperformed, at least 90% and more preferably at least about 95%, and mostpreferably at least about 97%, of the starting material is convertedinto salable product. This proportion far exceeds the short-run yieldobtainable with conventional systems. Second, the systems and methods ofthe invention allow a very rapid changeover between individual products.This is especially the case when use is made of the preferred controlapparatus and die assembly hereof. Third, the systems of the inventionpermit the user to vary the residence time of material in thepreconditioner during the course of an extrusion run while maintaining aconstant output to the extruder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a quick-changeover extruder systemin accordance with the invention;

FIG. 2 is a plan view of the system depicted in FIG. 1;

FIG. 3 is a side elevational view of another quick-changeover extrudersystem employing a vertically mounted preconditioner;

FIG. 4 is a fragmentary side view depicting the forward end of anextruder barrel and having the multiple-position die assembly of theinvention mounted thereon;

FIG. 5 is a sectional view taken along line 5—5 of FIG. 4 andillustrating further details of the extruder and multiple-position dieassembly;

FIG. 6 is a fragmentary top view of the extruder barrel andmultiple-position die assembly depicted in FIGS. 4-5;

FIG. 7 is a sectional view taken along line 7—7 of FIG. 6 andillustrating the multiple-position rotor forming a part of the dieassembly;

FIG. 8 is a front view of the die assembly of the invention, shown withthe front cover plate thereof removed so as to depict a rack and piniondrive for the die assembly;

FIG. 9 is a fragmentary side view of the forward end of one dieassembly, illustrating further details of the rack and pinion drive;

FIG. 10 is a schematic box diagram illustrating the control assembly forthe extruder system of the invention;

FIG. 11 is a flow diagram illustrating a portion of the preferredcontrol software used in operating the extruder system of the invention;

FIG. 12 is to be considered in conjunction with FIG. 11 and is anotherflow diagram illustrating the remaining portion of the preferred controlsoftware; and

FIG. 13 is a schematic box diagram illustrating the control assembly forthe dryer system of the invention; and

FIG. 14 is a flow diagram illustrating the preferred control softwareused in controlling the operation of the dryer system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawings and particularly FIGS. 1-2, a representativeextruder system 20 in accordance with the invention is illustrated.Broadly speaking, the system 20 includes an extruder assembly 21comprising a bin assembly 22 for receiving, handling, and feeding of drymaterials, a preconditioner 24, extruder 26, and specialized dieassembly 28. The output from extruder 26 is delivered to a dryer system29. As will be explained in more detail, the system 20 is controlled bymeans of a programmable logic controller 30 (see FIGS. 10 and 13) whichis operatively coupled with components of the system.

The Extruder Assembly

The bin assembly 22 includes an upper surge bin 32 equipped with aninlet 34 and an outlet 36. A selectively actuatable slide gate mechanism38 is provided adjacent the outlet 36 for opening and closing the latterduring operation of the system 20. A conventional product handlingsystem (not shown) is typically coupled to the inlet 34 of surge bin 32,in order to deliver dry ingredients thereto.

The assembly 22 also includes a live bottom bin 40 positioned beneaththe surge bin 32. In this connection, it will be observed that abox-type frame 42 is secured to surge bin 32 and supported by rails 44.The bin 40 is supported on the frame 42 by means of conventional loadcells 46. The inlet 48 of the bin 40 is coupled to the outlet 36 ofsurge bin 32 so that when the gate mechanism 38 is opened, material mayflow directly from the surge bin into the live bottom bin. The bin 40includes an outlet 50 which is coupled to an elongated, variable speedauger-type feed screw 52. The feed screw is powered by means of driveassembly 54 and has an outlet 56.

The preconditioner 24 is preferably of the type described in U.S. Pat.Nos. 4,752,139 and 5,161,888, incorporated by reference herein.Generally speaking, the preconditioner 24 is in the form of an elongatedtubular body 58 presenting an inlet 60 and an outlet 62. A pair ofelongated drive shafts (not shown) are situated within body 58 and arerotated at different speeds through a drive unit 64. The shafts supportoutwardly extending paddle-type mixers, which are strategically orientedso as to control the flow of material through the preconditioner bodyand to achieve adequate residence time therein so that the material isproperly moisturized and heated before entering the extruder 26. Inaddition, the preconditioner 24 is equipped with steam injectors 66 andwater injectors 68. The injectors 66, 68 are connected to conventionalflow meter control valves 66 a and 68 a (FIG. 10). As illustrated, thepreconditioner 24 is supported on four upright comer frame members 70each having a load cell 72 thereon. The four load cells 72 are in turnsupported on rigid crossframe members 74 and underlying crossrails 76.

An important feature of the present invention is the provision of avariable speed, variable output screw-type discharge feeder 78 equippedwith a variable frequency drive 80 (FIG. 10) between the outlet 62 ofpreconditioner 24 and the inlet of extruder 26. As will be understood,the feeder 78 has an inlet and an outlet. The feeder 78 is mountedadjacent the underside of preconditioner body 58 as shown, with theoutlet thereof coupled to a depending tubular 82. The 82 is alsoprovided with a bypass valve 84 operated through a position controller86 (FIG. 10) so that improperly preconditioned material may be divertedfrom the extruder 26, typically during initial startup of the system 20.

The extruder 26 includes an elongated, tubular barrel 88 made up ofend-to-end interconnected barrel heads 89 (see FIG. 5) and presenting aninlet 90 and an outlet end 92. An elongated, axially rotatable,helically flighted auger screw 93 made up of interconnected screwsections 93 a is situated within the barrel 88 and is operable to movematerial received into inlet 90 along the length of the barrel 88 forultimate extrusion through the die assembly 28. The internal screw isdriven through a drive assembly 94, the latter being controlled througha conventional speed controller 96. The extruder barrel 88 also hassteam and water injectors 98, 100 along the length thereof, with thelatter being controlled by associated flow meter control valves 102, 104(FIG. 10).

As those skilled in the art will readily understand, the barrel 88 andinternal screw are configured to cooperatively generate appropriatelevels of heat and shear to achieve the desired degree of extrusionprocessing. For example, the interconnected heads 89 may be configuredto present internal ribs 89 a, and steam locks 106 may be interposedbetween individual screw sections 93 a. Such processing can also beaided and controlled by steam and/or water injection through theinjectors 98, 100, and also by the use of externally jacketed barrelheads 89 permitting circulation of heating or cooling media therethroughfor indirect temperature control. Although the depicted embodiment is asingle screw extruder, twin screw units could also be employed.

The die assembly 28 is operatively connected to outlet end 92 ofextruder barrel 88 and is in communication with the interior of thelatter. The assembly 28 broadly includes a primary tubular head 108presenting three spaced apart outlet openings 110, 112 and 114, a rotor116 housed within the head 108, a drive assembly 118 operatively coupledwith rotor 116 in order to selectively rotate the latter and a hingemount assembly 120 permitting movement of the entire assembly 28 towardand away from barrel 88.

In detail, the head 108 includes a rearwardly flanged block 121presenting a pair of spaced apart, apertured sidewalls 122, 124, and isnormally secured to the endmost head 89 of barrel 88 by screws 126; asshown, the opening 110 is formed in sidewall 122, whereas the opposedopening 112 is formed in sidewall 124. The block 121 also presents a topwall 128 extending between the sidewalls 122, 124, as well as a bottomwall 130. As illustrated in FIGS. 5 and 7, an elongated dischargeopening 114 is formed in bottom wall 130. A discharge chute 132 issecured to bottom wall 130 in registration with the opening 114. An endplate 134 extends between the sidewalls 122, 124 and is secured theretoby screws 136.

A pair of frustoconical die extension mounts 138, 140 are respectivelymounted on a corresponding side plate 122, 124, in registry with theassociated opening 110, 112. Each such mount 138, 140 has an outermostapertured mounting flange 142 configured to permit interconnection of adie plate 144, 146 thereon (plates 144, 146 are referred to as dies Aand B in FIG. 10). Such die plates are themselves conventional, andinclude a plurality of extrusion openings 148 and 150 therethrough, andhave a central, outwardly extending knife mount shaft 152 or 154.

The rotor 116 is located within head 108 and includes a substantiallyannular in cross-section body 156 having a rear wall 158 with a centralproduct entrance opening 159 formed therein, and a forwardly extendingannular wall 160 having an outlet opening 161 therein. An arcuate,elbow-shaped passageway 162 extends between and interconnects the rotoropenings 159, 161. As best seen in FIG. 7, the rotor body 156 issupported for rotation on an upper arcuate surface 164 formed in the topof block 121, and on relatively small surfaces 166, 168 formed in thesidewalls 122, 124 immediately below the openings 110, 112. Theeffective surface areas presented by these lower supporting surfaces166, 168 are each less than the effective width of the outlet openingdefined by passageway 162. Thus, during rotation of the rotor 116 aswill be described between its operative positions, the passageway 162can never be completely blocked, thereby eliminating the possibility ofpotentially destructive pressure buildups within the die assembly 28.

The drive assembly 118 includes a pinion gear 170 secured to theoutboard face of rotor body 156 by means of screws 172. The outer faceof the gear 170 has a continuous bearing raceway 174, which cooperateswith a similar raceway formed in end plate 134; bearings 176 areemployed between the end plate 134 and gear 170 to guide the rotation ofrotor body 156. As best seen in FIGS. 5 and 8, an elongated, uprightrack 178 is in meshed, driving engagement with the gear 170. The rack178 is mounted for up and down reciprocation by means of a rack guideplate 180 affixed to sidewall 124 via screws 182.

The overall drive assembly further includes a piston and cylinder unit184 including a reciprocal piston rod 186 secured to the upper end ofrack 178 by a clevis 188. The unit 184 is supported on block 121 bymeans of an upstanding mount 190. In particular, the mount 190 includesa base plate 192 which is affixed to the upper surface 128 of block 121by mounting screws 194. The upper end of mount 190 affords aconventional pivotal connection for the cylinder of unit 184. While arack and pinion drive as shown provides greater changeover speed, insome cases it is preferred to use a gear motor and pinion drive in lieuof the depicted rack and pinion.

The purpose of drive assembly 118 is to selectively rotate rotor 116 sothat the outlet of passageway 162 will come into registry with eitherthe die outlet openings 110 or 112, or discharge opening 114. In orderto control such movement, the assembly 118 includes conventionalposition switches 196, 198 illustrated in FIG. 10.

The hinge mounting assembly 120 has a rearmost L-shaped mounting bracket200 secured to barrel 88, with a forwardly extending plate 202 affixedthereto and supporting a rear hinge pin 204. The forward end of theassembly 120 has a dogleg connector plate 206 affixed to the adjacentflange of the forwardmost barrel head 89 and head 108. This connectorsupports a forward hinge pin 208. A spanning plate 210 extends betweenand is coupled to the hinge pins 204, 208 to complete the hingeconstruction.

Turning again to FIG. 2, it will be observed that a pair of motor drivenrotary knife devices 212, 214 are respectively located adjacent acorresponding one of the die plates 144, 146. These knife devices areentirely conventional, and include rotary, power driven knife bladesmounted on the die plate shafts 152, 154 described previously. Inaddition, these devices have associated speed controls 216 and 218 (FIG.10).

Attention is next directed to FIG. 3, which depicts another extrudersystem 220 which is in most respects identical with system 20.Accordingly, like parts and components in FIGS. 1 and 3 are similarlynumbered. However, in this case, the extruder assembly 221 haspreconditioner 24 mounted in a vertical orientation, rather than thehorizontal orientation of FIG. 1. Such mounting requires a slightlydifferent preconditioner mounting frame 222 and different placement ofload cells 224, all as shown in FIG. 3. Moreover, a slightly differenttransition 226 is provided to the inlet of screw feeder 78 as comparedwith the FIG. 1 embodiment.

FIG. 10 illustrates in schematic form the controller 30 associated withthe extrusion system 20, as well as the interconnection of the variousextruder control devices with the controller 30. The actual wiring andsetup of the controller 30 is well within the skill of the art, in lightof the foregoing disclosure and the ensuing operational description.

Operation of the Extruder Assembly

The general operation of the extruder assemblies 20 and 220 is known tothose skilled in the art. That is, in a typical extrusion operation, drymaterials are fed to surge bin 32 in a pre-mixed condition. This is donethrough conventional pneumatic handling equipment. The dry material thenpasses through slide gate 38 and enters live bottom bin 40 where it iscontinuously mixed by a rotating blending element.

The material is then fed through the variable speed feed screw 52 intopreconditioner 24. In the preconditioner, the material is moisturizedand partially cooked by addition of steam and/or water while mixing iscarried out. Broadly speaking, conditions within the preconditionerinclude a maximum material temperature of from about 100-212° F., and aresidence time of from about 30 seconds-5 minutes. The preferredpreconditioner includes paddle components which retard the flow ofmaterial towards the preconditioner outlet in order to increaseresidence time. Where a horizontal preconditioner is used as in theembodiment of FIGS. 1-2, the majority of the paddle components along thelength of the preconditioner are set for such material retardation, butthe elements closely adjacent the outlet 62 are typically oriented forforward movement for material. In the case a vertically orientedpreconditioner as depicted in FIG. 3, all of the paddle elements wouldbe normally set for material flow retardation.

The provision of a preconditioner 24 with weighing devices 72, avariable speed, variable output feeder screw 52, and a variable speed,variable outlet discharge device 78, allows the user to vary theresidence time of the material in the preconditioner during the courseof an extrusion run. Heretofore, it has been impossible to vary thepreconditioner residence time on-the-go, and efforts to alter theresidence time have been limited to changing the type or position of themixing elements within the preconditioner between runs. Simply changingthe speed of the mixing elements is unworkable, because thissignificantly changes the characteristics of the output from thepreconditioner.

For example, if the extrusion system of the invention is operating at arate of 1 ton/hr. with a 2 minute preconditioner residence time, thenthe preconditioner 24 at any instant in time (after sustained operationis achieved) will contain about 67 lbs. of starting material. If theuser decides to increase the preconditioner residence time to 4 minutes,it is only necessary to increase the speed of the inlet feeder screw 52so that a greater mass flow rate into the preconditioner is established;however, during this period the discharge feeder 78 speed remainsunaltered so that the 1 ton/hr. overall extrusion system speed ismaintained. Additional material is then built up in the preconditioner24 (as monitored by the preconditioner load cells 72) until theinstantaneous weight of the starting material in the preconditionerdoubles to about 134 lbs., thus also doubling the initial residence timeto 4 minutes. At this point, the speed of inlet feeder screw 52 isreduced to its initial level, so that thereafter the residence time inthe preconditioner is 4 minutes. Of course, if a reduction inpreconditioner residence time is desired, the speed of inlet screwfeeder 52 is decreased until a desired instantaneous weight and thecorresponding residence time is achieved.

The preconditioned material is directed into and through the extruder26, while the screw 93 is rotated. As in the case of the preconditioner,a variety of operating conditions can be established in the extruder 26,depending upon the desired end product. For example, the maximummaterial temperature achieved in the extruder may range from 80-400° F.,with residence time of from 15 seconds-2 minutes. The pressure profilealong the barrel length is extremely variable, but maximum barrelpressures commonly range from about 100-800 psi. Auger rotational speedsare also variable, and may range from 50-2000 rpm. In the case of petfood production, typical maximum temperatures would be from about200-270° F. with a screw speed of from about 300-600 rpm.

The product is cooked and subjected to temperature and shear within theextruder, and is ultimately forced through a die plate for final cookingand forming. A large number of die plates can be employed, dependingupon cooking conditions desired and product shape.

Turning now to the details of operation of the systems of the invention,it will first be appreciated that the presence of a variable outputdischarge device such as the screw feeder 78 is an important aspect. Inorder to produce acceptable product from a high percentage of theoriginal starting materials, it is important that the screw feeder 78 bemaintained in a choked condition for as long as possible, i.e., thefeeder inlet must remain choke full. In this way, a constant and uniformflow of material is maintained to the extruder 26, in order to avoid,for as long as possible, a tailing off of product into and through theextruder which leads to varied and unpredictable cooking conditions andthus unacceptable end products.

Attention is directed to FIGS. 11-12 which illustrate preferred controlsoftware which would be incorporated into the controller 30. In thisdiscussion, it will be assumed that the user wishes to run two separateproducts A and B through the system 20 while avoiding significant wasteof the starting materials and simultaneously minimizing the changeovertime between the product runs.

Thus, as shown in FIG. 11 the system 20 is in operation producingproduct A (step 228). In this orientation, the system is set up forappropriate preconditioning and extruding of the product A materials(e.g., residence times, temperatures, pressures, and steam and waterinjection levels are established), and the die assembly 28 is set fordie A operations. After an initial start-up using the ingredient formulafor product A, the user would establish a substantially constant massflow rate of preconditioned material from the preconditioner 24 throughfeeder 78 and outlet 82 into extruder barrel 88. This assures thatduring the majority of the product A run, uniform end product isproduced.

At some point towards the end of the product run A, the operator in step230 selects a changeover option whereby the system 20 will be changedover to begin producing product B. The changeover selection entails astep 232 where the flow of product A dry ingredients to the surge bin isterminated and the surge bin is allowed to empty (step 234). Next, instep 236 the slide gate mechanism 38 is actuated to close the gate,thereby preventing any further flow of material from the surge bin 32 tothe live bottom bin 40. Thereupon, in step 238, the product B dryingredients are feed into the surge bin 32.

The live bin is next emptied as indicated in step 240 until the last ofthe product A ingredients are fed to and processed within preconditioner24. Such is known because of the load cells 46 which are coupled tocontroller 30. Also, steam injection into the preconditioner (step 242)is stopped, feeder 52 (step 244) is emptied, and water injection intothe preconditioner is terminated while the operation of the live bin 40is likewise terminated and the feeder 52 is shut down (step 246). Next,a time delay (step 248) is built into the software which permitspreconditioning of the final charge of product A ingredients within thepreconditioner. Towards the conclusion of the selected preconditioningtime, the preconditioner 24 is run in reverse (step 250). This is doneso as to push the preconditioned material forwardly toward thepreconditioner outlet so that the full choke on the feeder 78 ismaintained. In order to control this altered operation of thepreconditioner, the controller allows the reverse operation to continuefor a short period (step 252) whereupon the preconditioner is reversedfor normal operation (step 254) for a time period (step 256). At thispoint the program determines whether the preconditioner discharge rateis decreasing (step 258). This is known owing to the fact that the surgebin 32 and the preconditioner 24 are supported on load cells 46 and 72,thereby permitting calculation of the mass flow rate through thepreconditioner. If the discharge rate is not found to be decreasing,then the program causes the steps 250-256 to be repeated. This cyclingcontinues until the discharge rate is shown to decrease. When thishappens the preconditioner is run forwardly for a brief time (steps 260,262).

As the preconditioner is essentially cleared of the product A materialsthrough the completion of steps 260, 262, the slide gate mechanism 38 isactuated to open the gate between the bins 32, 40 and operation of thelive bin feeder mechanism is initiated (step 264). From this pointforward, two things occur simultaneously: first, the remaining fractionof the product A material is processed within extruder 26, and theproduct B materials are preconditioned. After the product A extrusion iscomplete, the preconditioned product B materials are then almostimmediately fed to the extruder for processing. In this way only aminimum of changeover time is required between the product A and productB runs.

In detail, the final stages of the product A run involve stopping thedischarge feeder 78 while steam injection to the extruder is alsoterminated (step 264). A time delay (step 266) then ensues, until waterinjection to the extruder is terminated, the rotation of screw 93 isstopped, and the operation of cutting knife A ends (step 268). Next thedisk valve is switched to its discharge position (step 269). These stepsof course occur toward the end of product flow through the extruder 26.After a suitable time delay (step 270), the valve mechanism 28 isswitched from die A to die B (step 272). This of course finallyconcludes the product A run, as referred to in step 274.

The movement of the die assembly from its extruding, die A positionfirst to its discharge position and then to its die B position iseffected by actuation of the piston and cylinder unit 184 forming a partof the die assembly 28. Referring to FIGS. 7 and 8, when it is firstdesired to shift the passageway 162 from the die A position, the pistonand cylinder assembly 84 is operated to retract rack 178 upwardlythereby rotating the rotor 116 through an arc of approximately 90° untilthe outlet end of passageway 162 comes into registry with lower opening114. In this condition, the remaining product A (which would typicallybe unacceptable) is diverted through the opening 114 for disposal. Afterall of the product A material is thus passed, the unit 184 is againactuated to move the passageway 162 through another 90° arc until thepassageway outlet comes into alignment with head opening 112. In thiscondition, the assembly 28 is of course ready for receiving andextruding the product B materials.

As indicated previously, during termination of the product A run throughthe extruder 26, the product B materials are being initially processedin the upstream components of the system 20. Referring again to FIG. 12,after the slide gate is opened in the live bin 40 and feeder 52 beginoperation, a time delay (step 266) is permitted so as to appropriatelyfill the preconditioner with the product B ingredients. At this point,steam injection to the preconditioner is begun (step 268) for a timeperiod (step 270), whereupon water injection is commenced (step 272). Bythe time that the preconditioner is essentially full (step 274), theextruder has essentially completed the extrusion of the product Amaterials and is ready to receive the product B ingredients. Just priorto delivery of the product B ingredients to the extruder, a waterinjection (step 276) for a time period (step 278) is carried out so asto flush remaining product A ingredients from the extruder; this ofcourse occurs during the time that the die assembly 28 is in itsdischarge position.

Next, the extruder is started by rotation of the screw 93 (step 280) andthe preconditioner 24 becomes full (step 282). the discharge feeder 78is then started and essentially constant flow conditions through thepreconditioner are established (step 284). After a short time delay(step 286) required to put the system 20 into its proper operationalmode for the step B product, the steam injection into the extruder isstarted, along with the operation of knife B (step 288). A further timedelay then ensues (step 290) whereupon the system 20 is in full andsustained product B operation (step 292).

As noted in FIG. 12, the controller 30 provides a managed period of noproduction between the product A and product B runs. This no-productionperiod is typically about equal to the preconditioner residence time forproduct A.

The operation of extruder assembly 221 is very similar to that describedabove. However, owing to the use of a vertically orientedpreconditioner, the described control loop of steps 250-258 is normallynot needed. This is because the feeder 78 in this embodiment isinherently maintained choke full through gravitation of the productwithin the preconditioner.

The Dryer Assembly

The dryer assembly 29 (FIG. 13) forms apart of the overall extrusionsystem 20 and is designed to operate in conjunction with extruderassembly 21 or 221. The assembly 29 is preferably in the form of amultiple stage vertical cascade dryer 300. Cascade dryers are known, andthose dryers commercialized by Wenger Manufacturing, Inc. of Sabetha,Kans. and especially preferred. Such dryers are illustrated in a 1999Wenger brochure entitled “Wenger Cascade Dryer” incorporated byreference herein.

Generally speaking, the preferred dryer 300 is divided into pluralvertically aligned stages (two of which (302, 304) are shown forillustrative purposes), each made up of a pair of interconnected decks306, 308 and 310, 312. An initial fill deck 314 is located atop stage302 as shown, while a final cooling deck 316 is disposed below stage304. The discharge from cooling deck 316 is received by good/rejectproduct conveyor 319.

Each of the decks 306-316 has a pivoting, multiple tray floor which isoperated via a corresponding hydraulic cylinder gate drives 306 a- 316 aso that the contents of each deck may be essentially instantly dumpedand delivered to the deck next below at appropriate times during drying.The drying stages 302, 304 include steam or gas air heaters for heatinginput air thereto, with selectively controllable fan units and dampersto control airflow therethrough. The cooling deck 316 uses ambientderived air for cooling and for this purpose also has a fan unit.Airflow through the dryer 300 alternates up and down between decks,while the recirculated air is ultimately exhausted through the top ofthe dryer.

Each of the dryer decks has a number of sensors 318 (typicallytemperature, humidity, pressure and product level sensors) associatedtherewith. Also, conventional motor drives for the deck dampers and fansare provided.

The conveyor 319 is controlled via a direction controller 320 whichallows the conveyor to be moved in opposite directions for separatinggood and reject product as will be explained.

Referring to FIG. 13, it will be seen that the gate drives 306 a- 316 a,deck sensors 318 and direction controller 320 are all connected to PLC.It will also be appreciated that the aforementioned motor drives andother conventional sensing/control components may also be coupled toPLC. Again, the connection of these components to the PLC isconventional and will be fully understood in light of the followingoperational description.

Operation of the Drying Assembly

Referring now to FIG. 14, the control software used in conjunction withdryer 29 is illustrated. In this discussion, it is assumed that the twoproducts A and B produced by the extruder as explained above inconnection with FIGS. 11-12 are to be successively dried and maintainedin a segregated condition.

Thus, at step 322, the dryer is in normal operation drying good productA. During this time, the appropriate air flows and air temperaturesthrough the dryer are established and consistent for drying of productA, and the conveyer 319 is operated to collect the good product A. Atsome point however, the extruder is no longer producing acceptableproduct A, which would typically correlate with step 258 (FIG. 11) ofthe extruder operation. At this point the operator informs the PLC thatthe remaining product A is reject product (step 324, FIGS. 13 and 14).The dryer then continues to operate in the usual fashion, and clears thefill deck 314 of good product A to allow the deck to receive the rejectproduct A (step 326). A time delay 328 then follows to permit the goodproduct A to pass downwardly through the dryer for collection as goodproduct. In step 330 the dryer is operating so that the decks thereofmove the reject product A through the dryer during the period of noextruder production described with reference to FIG. 312. Of course,during this cycle, the conveyer 319 is operated to move the rejectproduct A to a reject collection area.

At some point during the clearance of reject product A by the dryer, theextruder operation is commenced for product B (step 280, FIG. 12), andthe initial product B is fed to the dryer. The PLC determines whetherproduct B is entering the dyer, such being ascertained through thesensors 318 associated with fill deck 314 (step 332). If no product B isentering the dryer the program causes steps 328 and 330 to be repeated,until product B does enter the fill deck 314.

The initial product B is typically reject product and collects on thefill deck 314 (step 334). At some time in the product B extrusion, goodproduct is generated. At this point the operator informs the PLC thatthe product B is good (step 336). The dryer decks then cycle to clearthe fill deck 314 of reject product B, permitting good product B tocollect on the fill deck (step 338). At the same time, the dryer cooleroperates with both products A and B in separate ones of the decks306-316 below the fill deck (step 340).

Next, the reject product A reaches the cooling deck 316 (step 342) andsuch reject product is then delivered to the conveyer 319 which stilloperates in a reject product mode. After all of the reject product A hasbeen collected, the operation of conveyer 319 is changed to deliversubsequent product A to the good product collection point. Such goodproduct A (step 344) moves in stages through the dryer 29 until all ofthe good product A passes through the dryer. A time delay 346 thenensues permitting the dryer decks to cycle and discharge all of thereject product A following as the tailings from the product A extrusion(step 348).

The next following product in the dryer is reject product B, derivedfrom the initial startup of the extruder run B. When this reject productB reaches cooler deck 316 (step 350) a time delay 352 follows, allowingthe reject product B to be cycled through the dryer (step 354) forcollection as reject product. Having thus cleared all of the rejectproduct B, the dryer 29 is then in regular operation for drying of theremainder of the good product B (step 356).

It will thus be seen that the present invention provides methods andapparatus for extrusion processing which meet two important andheretofore unattainable goals. First, product runs are made possiblewherein substantially all of the starting material is processed asacceptable product, thereby eliminating the substantial waste common inprior systems. Second, it is now possible to run a series of relativelysmall runs in rapid succession, without undue down times between theruns.

We claim:
 1. An extruder system, comprising: an extruder having anelongated barrel with at least one axially rotatable, flighted augertherein, said barrel presenting a barrel inlet and a barrel outlet; adie assembly mounted on said barrel outlet; a preconditioner includingshiftable mixing elements therein and having a preconditioner inlet forreceiving material to be preconditioned, said preconditioner having apreconditioner outlet operatively coupled with said barrel inlet forfeeding preconditioned material from the preconditioner into the barrel;a bin assembly operatively coupled with said preconditioner inlet forfeeding said material to be preconditioned to said preconditioner inlet;and apparatus permitting selective alteration of the residence time ofsaid material within said preconditioner between a first residence timeand a second, predetermined residence time different than said firstresidence time, said apparatus including a variable output feeder deviceoperatively coupled with said preconditioner outlet, and a component forcontinuously weighing said preconditioner.
 2. The system of claim 1,said component comprising a load cell operatively coupled with saidpreconditioner.
 3. The system of claim 1, said apparatus operable todetermine the mass flow rate of material passing through saidpreconditioner, the system including a controller operatively coupledwith said apparatus and said extruder and said preconditioner forcontrolling the operation of the extruder system in response to saidmass flow rate determination.
 4. The system of claim 3, said controllerincluding a programmable microprocessor.
 5. The system of claim 1, saidpreconditioner comprising an elongated preconditioner body having saidelements therein, the longitudinal axis of said preconditioner bodybeing generally parallel with the longitudinal axis of said barrel. 6.The system of claim 1, said preconditioner comprising an elongatedpreconditioner body having said elements therein, the longitudinal axisof said preconditioner body being generally transverse relative to thelongitudinal axis of said barrel.
 7. The system of claim 6, saidpreconditioner being mounted in an upright, substantially verticalorientation above said barrel inlet.
 8. The system of claim 1, said dieassembly comprising a head having first and second spaced outlets, withfirst and second die members operatively coupled with the first andsecond die outlets respectively, there being a shiftable diverter forselectively and alternately diverting the flow of material from saidextruder outlet into and through the first or second die outlets.
 9. Thesystem of claim 1, said bin assembly including a surge bin and a livebottom bin coupled in series, said first detector assembly including afirst load cell being operatively coupled with said live bottom bin. 10.The system of claim 1, there being a variable speed, variable outputdischarge screw device between said preconditioner outlet and saidbarrel inlet.
 11. An extruder system, comprising: an extruder having anelongated barrel with at least one axially rotatable, flighted augertherein, said barrel presenting a barrel inlet and a barrel outlet; adie assembly mounted on said barrel outlet; a preconditioner includingshiftable mixing elements therein and having a preconditioner inlet forreceiving material to be treated, said preconditioner having apreconditioner outlet operatively coupled with said barrel inlet forfeeding preconditioned material from the preconditioner into the barrel;and apparatus permitting selective alteration of the residence time ofsaid material within said preconditioner between a first residence timeand a second, predetermined residence time different than said firstresidence time, said apparatus including a variable output feeder deviceoperatively coupled with said preconditioner outlet, and a component forcontinuously weighing said preconditioner.
 12. The system of claim 11,said component comprising a load cell operatively coupled with saidpreconditioner.
 13. The system of claim 11, said device comprising avariable speed, variable output discharge screw device between saidpreconditioner outlet and said barrel inlet.
 14. A method of operatingan extrusion system to process a quantity of material, said extrusionsystem including an interconnected preconditioner and extruder, saidextruder having an elongated extruder barrel having a barrel inlet and abarrel outlet and at least one elongated, axially rotatable lightedscrew within the barrel, said preconditioner having a body with apreconditioner inlet, a preconditioner outlet, and shiftable mixingelements within the preconditioner body, said preconditioner outletbeing operatively coupled with said barrel inlet for passage ofpreconditioned material from the preconditioner into the extruderbarrel, said method comprising the steps of: initially processing saidquantity of material by passing material from said quantity thereof intosaid preconditioner inlet and through said preconditioner while shiftingsaid mixing elements, and causing the preconditioned material to passfrom the preconditioner outlet and into and through said extruder, untila substantial fraction of said quantity of material is processed, duringsaid initial processing step, establishing a substantially constant massflow rate of preconditioned material from said preconditioner outlet andinto said barrel inlet; after said substantial fraction of said quantityof material is processed in said initial processing step, continuing topass additional material from said quantity thereof into saidpreconditioner until substantially the remainder of said quantity ofmaterial is within said preconditioner body; and while a portion of saidsubstantial remainder of said quantity of material is within saidpreconditioner body, altering the operation of said preconditioner tosubstantially maintain said substantially constant mass flow rate ofmaterial passing through the preconditioner outlet and into said barrelinlet.
 15. The method of claim 14, including the step of continuing torun said preconditioner until substantially all of said remainder ofsaid quantity of material is passed into said barrel inlet.
 16. Themethod of claim 14, including the step of determining said mass flowrate of material passing through the preconditioner outlet during saidaltered operation of said preconditioner.
 17. The method of claim 14,including the step of determining said mass flow rate of materialpassing through the preconditioner outlet, during said initialprocessing step and said continued passage step.
 18. The method of claim16, including the step of weighing said preconditioner as at least apart of said mass flow rate determining step.
 19. The method of claim14, said mixing elements being mounted on an axially rotatable shaft,said operation-altering step comprising the step of reversing thedirection of rotation of said shaft, as compared to the rotation thereofduring said initial processing step.
 20. A method of sequentiallyextrusion processing quantities of first and second different materialsin an extrusion system, said extrusion system including aninterconnected preconditioner and extruder, said extruder having anelongated extruder barrel having a barrel inlet and a barrel outlet andat least one elongated, axially rotatable flighted screw within thebarrel, said preconditioner having a body with a preconditioner inlet, apreconditioner outlet, and shiftable mixing elements within thepreconditioner body, said preconditioner outlet being operativelycoupled with said barrel inlet for passage of preconditioned materialfrom the preconditioner into the extruder barrel, said method comprisingthe steps of: initially processing said quantity of said first materialby passing the first material from said quantity thereof into saidpreconditioner inlet and through said preconditioner while shifting saidmixing elements, and causing the preconditioned first material to passfrom the preconditioner outlet and into and through said extruder, untila substantial fraction of said quantity of first material is processed,during said initial processing step, establishing a substantiallyconstant flow rate of preconditioned first material from saidpreconditioner outlet and into said barrel inlet; after said substantialfraction of said quantity of first material is processed in said initialprocessing step, continuing to pass additional first material from saidquantity thereof into said preconditioner until substantially theremainder of said quantity of material is within said preconditionerbody; while a portion of said substantial remainder of said quantity offirst material is within said preconditioner body, altering theoperation of said preconditioner to substantially maintain saidsubstantially constant flow rate of first material passing through thepreconditioner outlet and into said barrel inlet and passing saidsubstantial remainder of said first material into said barrel inlet;thereafter passing quantities of said second material into saidpreconditioner inlet and through said preconditioner body forpreconditioning of said second material quantities; and passing saidpreconditioned second material quantities into said barrel inlet andthrough said extruder for processing of said second material.
 21. Themethod of claim 20, including the step of determining the mass flow rateof said first material passing through the preconditioner outlet duringsaid altered operation of said preconditioner.
 22. The method of claim21, including the step of continuously determining said mass flow rateof first material passing through the preconditioner outlet, during saidinitial processing step and said continued passage step.
 23. The methodof claim 21, including the step of weighing said preconditioner as atleast a part of said mass flow rate determining step.
 24. The method ofclaim 20, said mixing elements being mounted on an axially rotatableshaft, said operation-altering step comprising the step of reversing thedirection of rotation of said shaft, as compared to the rotation thereofduring said initial processing step.
 25. An extruder system comprising:an extruder including an elongated barrel with an inlet, an outlet, atleast one axially rotatable screw within the barrel, and a die adjacentsaid barrel outlet; a preconditioner including a mixing body with aseries of shiftable mixing elements therein, said body presenting aninlet and an outlet, with said outlet operatively coupled with saidbarrel inlet; and apparatus permitting selective alteration of theresidence time of said material within said preconditioner between afirst residence time and a second, predetermined residence timedifferent than said first residence time, said apparatus including avariable output feeder device operatively coupled with saidpreconditioner outlet, and a component for continuously weighing saidpreconditioner.
 26. The system of claim 25, said component comprising aload cell.
 27. A preconditioner assembly comprising: a hollow mixingbody including a material inlet, a material outlet, and a series ofshiftable mixing elements within the body, said body operable to receivematerial through said inlet, to precondition material and to deliverpreconditioned material to said outlet; and apparatus permittingselective alteration of the residence time of said material within saidpreconditioner body between a first residence time and a second,predetermined residence time different than said first residence time,said apparatus including a variable output feeder device operativelycoupled with said preconditioner outlet, and a component forcontinuously weighing said preconditioner.
 28. The preconditioner ofclaim 27, said component comprising a load cell.
 29. The preconditionerof claim 27, said apparatus including a controller, said dischargedevice and said component coupled with said controller.
 30. In a methodof operating an extrusion system having a preconditioner having an inletand an outlet and an extruder coupled with said outlet to receivepreconditioned material from the outlet, including the steps ofcontinuously operating the preconditioner to deliver preconditionedmaterial to the extruder at a substantially constant first rate andafter a first residence time within the preconditioner, and continuouslyoperating the extruder to process said preconditioned material, theimprovement comprising the steps of varying the residence time of saidmaterial within the preconditioner to a second predetermined residencetime different than said first residence time during said continuousoperation of the preconditioner and extruder.
 31. The method of claim30, said residence time varying step comprising the steps ofcontinuously weighing said preconditioner and varying the mass flow rateof material passing into said preconditioner inlet while maintaining themass flow rate of material leaving the preconditioner outlet at a levelto effect said change of the residence time.
 32. The method of claim 31,including a variable output discharge device coupled with said outlet,said flow rate-varying step comprising the step of varying the output ofthe discharge device.
 33. The method of claim 30, including a variableoutput feeding assembly coupled to said preconditioner inlet, saidresidence time varying step comprising the step of varying the feeder tovary the mass flow rate of material entering the preconditioner.
 34. Abin and preconditioner assembly comprising: a bin assembly for holdingmaterial to be processed; a preconditioner including a hollow mixingbody having an inlet and an outlet, said inlet operatively coupled withsaid bin assembly for continuous passage of said material from the binassembly and into said preconditioner body; and apparatus permittingselective alteration of the residence time of said material within saidpreconditioner between a first residence time and a second,predetermined residence time different than said first residence time,said apparatus including a variable output feeder device operativelycoupled with said preconditioner outlet, and a component forcontinuously weighing said preconditioner.
 35. The assembly of claim 34,said component including a load cell operatively coupled with saidpreconditioner.
 36. The method of claim 30, including the step ofvarying said residence time while maintaining the delivery ofpreconditioned material to the extruder at said substantially constantfirst rate.
 37. In a method of operating an extrusion system having apreconditioner having an inlet and an outlet and an extruder coupledwith said outlet to receive preconditioned material from the outlet,including the steps of continuously operating the preconditioner andextruder to process material passes serially through the preconditionerand extruder, the improvement comprising the steps of varying theresidence time of said material within the preconditioner during saidcontinuous operation of the preconditioner and extruder, said residencetime varying step comprising the steps of continuously weighing saidpreconditioner and varying the mass flow rate of material passing intosaid preconditioner inlet while maintaining the mass flow rate ofmaterial leaving the preconditioner outlet at a level to effect saidchange of the residence time.
 38. In a method of operating an extrusionsystem having a preconditioner having an inlet and an outlet and anextruder coupled with said outlet to receive preconditioned materialfrom the outlet, including the steps of continuously operating thepreconditioner to deliver preconditioned material to the extruder at asubstantially constant first rate and after a first residence timewithin the preconditioner, and continuously operating the extruder toprocess said preconditioned material, the improvement comprising thesteps of varying the residence time of said material within thepreconditioner to a second predetermined residence time different thansaid first residence time during said continuous operation of thepreconditioner and extruder, said residence time varying step comprisingthe steps of varying the flow rate of material passing into saidpreconditioner inlet while maintaining the flow rate of material leavingthe preconditioner outlet at a level to effect said change of theresidence time.
 39. The method of claim 38, including the steps ofvarying the mass flow rate of material passing into said preconditionerwhile maintaining the mass flow rate of material leaving thepreconditioner outlet at a level to effect said change of the residencetime.
 40. The assembly of claim 35, including first and second loadcells operatively coupled with said bin assembly and preconditionerrespectively.
 41. The system of claim 2, including first and second loadcells operatively coupled with said bin assembly and preconditionerrespectively.